ci: Skip VPP tests if needed

ci: Skip VPP tests if needed

If VPP can't be executed properly, then VPP tests will be skipped
for VERIFY and MERGE jobs. It sometimes happens, that VPP can't
be executed at builders used for VERIFY & MERGE jobs execution.
These failures are not caused by patches themselves, but they
are blocking standard review & merge process. Thus VPP tests
will be suppressed in case that VPP can't be started at all.
This change is not related to DAILY job, which is executed
at POD dedicated to VSPERF project. It means that VPP tests
are always executed by DAILY job.

Change-Id: I4752601561b94a82482c403305bc3f24779f538b
Signed-off-by: Martin Klozik <martinx.klozik@intel.com>
Reviewed-by: Al Morton <acmorton@att.com>
Reviewed-by: Christian Trautman <ctrautma@redhat.com>
Reviewed-by: Sridhar Rao <sridhar.rao@spirent.com>
Reviewed-by: Trevor Cooper <trevor.cooper@intel.com>